DESCRIPTION: (Candidate's Abstract) Hypoxia is thought to play a role in the pathogenesis of several ocular diseases. It is Clear that hypoxia is the driving force behind the development of retinal neovascularization (NV) in patients with ischemic retinopathies, including diabetic retinopathy and central and branch retinal vein occlusions. Macular edema is another major cause of decreased vision in ischemic retinopathies and it is suspected, but not yet proven that hypoxia plays a critical role. Likewise, it is suspected, but not yet proven, that hypoxia contributes to the development of choroidal neovascularization (CNV) in patients with age-related macular degeneration (AMD). Supplemental inspired oxygen provides a means to enhance oxygenation in the retina and choroid. We propose to use supplemental inspired oxygen to test several hypotheses related to the role of hypoxia in ocular NV and macular edema. The following experimental questions will be addressed. (1) Does supplemental inspired oxygen cause regression or slow progression of retinal NV that is not high risk in patients with diabetic retinopathy? (2) Does supplemental oxygen cause improvement in macular edema in patients with ischemic retinopathy? (3) Does supplemental oxygen cause stabilization or improvement in AMD patients with predominantly occult subfoveal CNV? (4) Does supplemental oxygen decrease recurrent CNV in AMD patients with predominantly classic CNV treated with photodynamic therapy? The answers to these questions will provide important insights into the pathogenesis of retinal diseases that could lead to the development of new treatments.